The present disclosure relates to the molding of articles of manufacture. More particularly, the disclosure relates to an improved core locking assembly that enables injection molding tooling to be selectively oriented and secured for injection molding preforms or sections used in the manufacture of ophthalmic lenses, such as contact lenses and intraocular lenses. The improved core locking assembly is particularly applicable to asymmetric tooling used for injection molding preforms that are ultimately used in forming asymmetric ophthalmic lenses, such as toric contact lenses, and will be described with particular reference thereto. It is to be appreciated, however, that the improved core locking assembly and apparatus related thereto may have utility in a variety of other similar environments and applications.
One method in practice for making ophthalmic lenses, including contact lenses and intraocular lenses, is cast molding. Cast molding of ophthalmic lenses involves depositing a curable mixture of polymerizable lens materials, such as monomers, in a mold cavity formed by two assembled mold sections, curing the mixture, disassembling the mold sections and removing the molded lens. Other post-molding processing steps, for example, hydration in the case of hydrogel lenses, may also be employed. Representative cast molding methods are disclosed in U.S. Pat. No. 5,271,875 (Appleton et al.); U.S. Pat. No. 4,197,266 (Clark et al.); U.S. Pat. No. 4,208,364 (Shepherd); U.S. Pat. No. 4,865,779 (Ihn et al.); U.S. Pat. No. 4,955,580 (Seden et al.); U.S. Pat. No. 5,466,147 (Appleton et al.); and U.S. Pat. No. 5,143,660 (Hamilton et al.).
When cast molding between a pair of mold sections, typically one mold section, referred to as the anterior mold section or preform, forms the anterior convex, optical surface of the ophthalmic lens and the other mold section, referred to as the posterior mold section or preform, forms the posterior concave, optical surface of the ophthalmic lens. The anterior and posterior mold sections are generally complimentary in configuration. They are joined together during the molding process to form a lens forming or molding cavity. Once the lens is formed, the mold sections or preforms are separated and the molded lens is removed. The anterior and posterior mold sections are usually used only once for casting a lens prior to being discarded due to the significant degradation of the optical surfaces of the mold sections that often occurs during a single casting operation.
Formation of the mold sections used in casting occurs through a separate molding process prior to cast molding. In this regard, the mold sections are first formed by injection molding a resin in the cavity of an injection molding apparatus. More particularly, mounted in the injection molding apparatus are tools for forming the mold sections. Typically, the tools are fitted into mold plates in the injection molding machine and the mold sections are produced by injection molding a selected resin between opposed sets of injection molding tools. The tools are typically made from brass, stainless steel, nickel, or some combination thereof and, unlike the mold sections which are used only once, the injection molding tools are used again and again to make large quantities of mold sections.
The injection molding tools are typically formed in accordance with the specification of corresponding ophthalmic lens surfaces to be formed on or by the mold sections. That is, the ophthalmic lens being produced determines the specific design of the mold sections. The needed mold section parameters, in turn, determine the design of the corresponding injection molding tools. Thus, for example, when producing an ophthalmic lens having at least one asymmetric surface, the mold sections and molding tools would include corresponding asymmetric mold surfaces. In any case, the injection molding tools are typically manufactured to extremely high specifications and/or tolerances so that no roughness or surface defects are transferred to the mold sections being made from the tools. Any such defects on the mold sections, particularly on an optical surface of a mold section, is likely to be transferred to, and appear on, the finished lens during the cast molding operation.
Each mold section, whether it be a posterior mold section or an anterior mold section, includes an optical surface (posterior optical surface on a posterior mold section and anterior optical surface on an anterior mold section) that forms a surface of the ophthalmic lens, as well as a non-optical surface. When injection molding the mold section, the injection molding apparatus typically includes an optical tool assembly for forming the optical surface of the mold section and a non-optical tool assembly for forming the non-optical surface of the mold section. When the lens to be formed includes an asymmetric surface, the mold section optical surface used to form the asymmetric lens surface and the optical tool assembly used to form the mold section optical surface each may include corresponding asymmetric surfaces.
One example of a lens having an asymmetric surface is a toric contact lens, which is sometimes employed for correcting an astigmatism of the cornea. Toric contact lenses often include a toric surface (i.e., an asymmetrical surface) defined along a toric axis and a ballast used to properly orient the toric axis over a corresponding astigmatism of one's cornea. Another example of an asymmetric lens is a multifocal contact lens. These and other types of asymmetric lenses can present unique manufacturing challenges, particularly as compared to spherical or symmetrical lenses, due to their inclusion of at least one rotationally asymmetric surface. One such problem can occur during set-up of the injection molding tools used to make the mold sections which are then subsequently used to form the asymmetric lenses.
For example, it has been found that during injection molding of mold sections having asymmetric surfaces, such as those used for forming toric contact lens, the flow dynamics of the fluid mold material (i.e., the molten resin used to form the mold sections) over the tooling assembly's molding surface varies depending on the orientation of the asymmetric molding surface relative to the flow direction of the fluid mold material emanating from the gate of the injection molding apparatus. This is particularly problematic when asymmetric mold sections are formed in a plurality of mold cavities, which occur in multi-cavity injection molding machines and/or among a plurality of injection molding machines. Asymmetric mold sections formed in different cavities can have varying optical surfaces formed as a result of the mold sections being formed in cavities each having a different rotational orientation between the asymmetric molding surface and the gate through which molten resin enters the mold cavity. These variations are ultimately transferred to the cast molded lenses causing the lenses, in some instances, to be scrapped.
Variations in the cast molded lenses can also occur in lenses formed from mold sections being injection molded from a single mold cavity. This could occur when the optical tool assembly of the injection molding apparatus is formed of multiple components. For example, the optical tool assembly could include an optical insert having the asymmetric optical molding surface thereon being removably secured, such as by threaded engagement, to a core member or optical tool holder. When the optical insert is removed and reattached (or replaced), rotational positioning of the optical insert relative to the core member is not likely to be the same as before removal, thus the rotational positioning relative to the gate is likely to be different. As a result, mold sections molded before removal of the optical insert are likely to have asymmetric surfaces that are different than those of mold sections molded after removal and replacement of the optical insert. It may furthermore be desirable to align the injection molding gate with any type of marking intentionally placed on the optical or non-optical part of the mold section. It may furthermore be desirable to align a particular feature or marking on one of the optical or non-optical tools or components thereof with a particular feature or marking on the opposing optical or non-optical tool or component thereof.
Prior improvements to optical tool assemblies have enabled a threadedly connected optical insert having an asymmetrical molding surface to be selectively and rotatably positionable relative to an injection molding gate. However, despite previous improvements, there is still a need for any additional improvements that more easily enable either one or both of the optical insert and non-optical insert to be selectively and rotatably positionable after installation of the non-optical or optical insert. By enabling quick selective rotation of either one or both of the optical and non-optical inserts, the set-up, i.e., the relative positioning of the inserts, particularly before and after the changing of inserts, is more consistent and controlled. This allows, for example, for the selective positioning of an asymmetric or other mold feature of one insert relative to the opposite tool insert and/or to an injection molding gate, for example. As a further example, parameters such as mold part thickness, which may change depending on the rotational positioning of the opposing inserts, may therefore be more precisely controlled. Thus, improvements that allow the non-optical and/or optical insert to be toggled between being rotatably fixed in a selected position and being rotatably movable to a selected rotational position are deemed desirable.